BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Can a component dropped on a from delete itself?          BorlandTalk.com Forum Index -> C++ Builder (VCL Components Development) View previous topic :: View next topic   Author Message Larry Griffiths Guest Posted: Thu Feb 15, 2007 1:41 am    Post subject: Can a component dropped on a from delete itself? I am writing a TCustomControl descendant and I am able to drop it on a form. The Goal: This descendant will look for any other descendants of its type on its parents Control list and delete itself if one already exists. I tried Owner->RemoveComponent( this ) and it appears to work but the component seems to still be drawing itself on the form. I added Parent->RemoveControl but this causes exceptions. The Question: How can a TCustomControl descendant remove itself from the form at design time? Back to top Remy Lebeau (TeamB) Guest Posted: Thu Feb 15, 2007 1:50 am    Post subject: Re: Can a component dropped on a from delete itself? "Larry Griffiths" <nospame (AT) nowhere (DOT) com> wrote in message news:45d36690$1 (AT) newsgroups (DOT) borland.com... Quote: This descendant will look for any other descendants of its type on its parents Control list and delete itself if one already exists. Do not delete it at all. Inside the constructor, throw an exception instead. That will abort the construction. Quote: I tried Owner->RemoveComponent( this ) and it appears to work but the component seems to still be drawing itself on the form. As it should be. You did not actually delete the component. All you did was remove its memory management from the Owner's list. Besides, removing it from the Owner is not the right thing to do anyway. What if the user creates the component dynamically at runtime? There may not be an Owner assigned at all. Gambit Back to top Larry Griffiths Guest Posted: Thu Feb 15, 2007 8:01 pm    Post subject: Re: Can a component dropped on a from delete itself? Thanks Gambit, What I had come up with was the following but I think the Parent Propery is filled in when it goes through the constructer. and may be the better route to go... void __fastcall TSomeClass::ValidateContainer(TComponent* AComponent) { // The first time this is called, AComponent is Owner. // The Second time this method is called, AComponent is Parent. if ( ValidateContainerCount++ ) { TWinControl *WC = dynamic_cast<TWinControl*>( AComponent ); if( WC ) { for ( int ix = 0; ix < WC->ControlCount; ix++ ) { if( TSomeClass already in Parents list ) { // Do not allow the component to be added to the form. throw Exception( Message ); } "Remy Lebeau (TeamB)" <no.spam (AT) no (DOT) spam.com> wrote in message news:45d36804 (AT) newsgroups (DOT) borland.com... Quote: "Larry Griffiths" <nospame (AT) nowhere (DOT) com> wrote in message news:45d36690$1 (AT) newsgroups (DOT) borland.com... This descendant will look for any other descendants of its type on its parents Control list and delete itself if one already exists. Do not delete it at all. Inside the constructor, throw an exception instead. That will abort the construction. I tried Owner->RemoveComponent( this ) and it appears to work but the component seems to still be drawing itself on the form. As it should be. You did not actually delete the component. All you did was remove its memory management from the Owner's list. Besides, removing it from the Owner is not the right thing to do anyway. What if the user creates the component dynamically at runtime? There may not be an Owner assigned at all. Gambit Back to top Remy Lebeau (TeamB) Guest Posted: Fri Feb 16, 2007 12:07 am    Post subject: Re: Can a component dropped on a from delete itself? "Larry Griffiths" <nospame (AT) nowhere (DOT) com> wrote in message news:45d46849$1 (AT) newsgroups (DOT) borland.com... Quote: What I had come up with was the following but I think the Parent Propery is filled in when it goes through the constructer. The Parent property is not set until after the constructor has exited. Quote: may be the better route to go... For design-time created instance, the Owner that is passed to the constructor will be the same control that will be assigned as the Parent, so you can validate the Owner immediately. For run-time created instances, however, you will have to wait for the Parent property to be set, since the user could pass a NULL Owner, or a different Owner than the Parent. Try the following (untested): class TSomeClass : public TCustomControl { typedef TCustomControl inherited; private: bool FHasInitialOwner; bool FSettingParent; protected: virtual void __fastcall SetParent(TWinControl *AParent); virtual void __fastcall ValidateContainer(TComponent* AComponent); public: __fastcall TSomeClass(TComponent *Owner); }; __fastcall TSomeClass::TSomeClass(TComponent *Owner) : TCustomControl(Owner) { FHasInitialOwner = true; //... } void __fastcall TSomeClass::SetParent(TWinControl *AParent) { FSettingParent = true; try { inherited::SetParent(AParent); } __finally { FSettingParent = false; } } void __fastcall TSomeClass::ValidateContainer(TComponent* AComponent) { if( ((AComponent->ComponentState.Contains(csDesigning)) && (!FHasInitialOwner)) || FSettingParent ) { TWinControl *WC = dynamic_cast<TWinControl*>(AComponent); if( WC ) { for( int ix = 0; ix < WC->ControlCount; ++ix) { if( dynamic_cast<TSomeClass*>(WC->Controls[ix] ) { // Do not allow the component to be added to the form. throw Exception("TSomeClass already exists"); } } } } } Gambit Back to top JD Guest Posted: Sun Feb 18, 2007 9:18 pm    Post subject: Re: Can a component dropped on a from delete itself? "Larry Griffiths" <nospame (AT) nowhere (DOT) com> wrote: Quote: [...] This descendant will look for any other descendants of its type on its parents Control list and delete itself if one already exists. It sounds as if you want only one copy of that control and if so, there is a much easier way than itterating all controls: Just use a global pointer. For example: TSingleInstance *ThisSingleInstance = NULL; //------------------------------------------------------------- __fastcall TSingleInstance::TSingleInstance(TComponent* Owner) : TComponent(Owner) { if( ThisSingleInstance ) { throw Exception("TSingleInstance : Only one instance of TSingleInstance is allowed per application."); } ThisSingleInstance = this; } //------------------------------------------------------------- ~ JD Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         BorlandTalk.com Forum Index -> C++ Builder (VCL Components Development) All times are GMT Page 1 of 1   Jump to: Select a forum C++ Builder Newsgroups----------------C++ BuilderC++ Builder (ActiveX)C++ Builder (Announcements)C++ Builder (Command Line Tools)C++ Builder DatabasesC++ Builder Databases (ADO)C++ Builder Databases (Desktop)C++ Builder Databases (InterBase Express)C++ Builder Databases (Multi-Tier)C++ Builder Databases (SQL Servers)C++ Builder (Graphics)C++ Builder (IDE)C++ Builder (Internet)C++ Builder (Internet Socket)C++ Builder (Internet Web)C++ Builder (Jobs)C++ Builder (Language)C++ Builder (Language C++)C++ Builder (Compatibility with MFC)C++ Builder (Native API)C++ Builder (Non-Technical)C++ Builder (Students)C++ Builder (Third Party Tools)C++ Builder (Upgrade)C++ Builder (VCL)C++ Builder (VCL Components Usage)C++ Builder (VCL Components Development)C++ Builder (VCL Usage)C++ Builder (WinAPI)C++ Builder Installation Delphi Newsgroups----------------Delphi (General)Delphi ActiveX Controls UsageDelphi ActiveX Controls DevelopmentDelphi As400Delphi DatabasesDelphi Databases (ADO)Delphi Databases (dbExpress)Delphi Databases (Desktop)Delphi Databases (InterBase Express)Delphi Databases (Multi-Tier)Delphi Databases (SQL Servers)Delphi DeploymentDelphi GraphicsDelphi IDEDelphi InternationalizationDelphi InternetDelphi Internet Isapi-WebBrokerDelphi Internet WebSnapDelphi Internet WinsockDelphi JobsDelphi Language BASMDelphi Language ObjectPascalDelphi Model Driven Architecture (General)Delphi Model Driven Architecture (Third Party)Delphi MultimediaDelphi Native APIDelphi Non-TechnicalDelphi ObjectPascalDelphi OLE AutomationDelphi OO designDelphi OpenToolsAPIDelphi Reporting-ChartingDelphi RTLDelphi StudentsDelphi TeamSourceDelphi Thirdparty ToolsDelphi Thirdparty Tools (General)Delphi Thirdparty Tools (IntraWeb)Delphi Thirdparty Tools (RaveReports)Delphi UpgradeDelphi VCLDelphi VCL ComponentsDelphi VCL Components UsingDelphi VCL Components WritingDelphi WebServices SOAPDelphi WinAPIDelphi XMLDelphi Installationcomp.lang.pascal.delphi.components.misccomp.lang.pascal.delphi.components.usagecomp.lang.pascal.delphi.components.writingcomp.lang.pascal.delphi.databasescomp.lang.pascal.delphi.misccomp.sources.delphi JBuilder Newsgroups----------------JBuilderJBuilder AnnouncementsJBuilder Applet IssuesJBuilder As400JBuilder CompilerJBuilder CORBA/RMIJBuilder DatabasesJBuilder DB SwingJBuilder DebuggerJBuilder DeploymentJBuilder DocumentationJBuilder EnterpriseJBuilder HandheldJBuilder IDEJBuilder JavaJBuilder JavaAPIJBuilder Java LanguageJBuilder Java SwingJBuilder Java BeansJBuilder Java Beans UsageJBuilder Java Beans DevelopmentJBuilder JBCLJBuilder JDataStoreJBuilder JobsJBuilder LinuxJBuilder MacintoshJBuilder & MobileSetJBuilder MultiLingual AppsJBuilder Non-TechnicalJBuilder OpenToolsJBuilder Servlets (JSP)JBuilder StudentsJBuilder Team DevelopmentJBuilder Thirdparty ToolsJBuilder UpgradeJBuilder Installation InterBase Newsgroups----------------InterBaseInterBase Bug DiscussionInterBase GeneralInterBase IBConsoleInterBase OpenSourceInterBase ReplicationInterBase SQLInterBase ThirdpartyInterBase Installation Miscellaneous Borland Newsgroups----------------AppCenterAppServerEnteraVisiBroker  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.